Dehairing of skins and hides



Patented Dec. 17, 1940 v UNITED STATES PATENT OFFICE DEHAIRING OF SKINSAND HIDES No Drawing. Application June 26, 1936,

- Serial No. 87,328

.24 Claims.

The present invention relates to the art of depilating or unhairinghides or skins.

In unhairing skins or hides it is usual to soak the hides or skins withthe assistance of various chemicals or treating agents to loosen thehair therein, so that such hair may be readily removed by scraping orother mechanical dehairing processes or to destroy or dissolve the hairaway from the skin or hide. a

The most frequent treating agent utilized in the dehairing of skins andhides is lime, with orwithout the addition of other alkaline materials,such as caustic soda.

These alkaline treatments are preferably carried out in such a mannerthat the hair of the skin or hide will be readily removed without injuryto the pelt, and the pelt so treated is then subjected to bating,puering and tanning processes to produce the final leather.

Instead of the alkaline treatment, for the purpose of loosening thehair, the skins or hides may also be subjected to a sweating process, in

as sodium sulphide, the form of arsenic sulphide known as red arsenic,and varioig amines such as methylamine. It has been found,howver,thatsuch sharpening agents can be used only in limited quantities becauseexcessive quantities result in damage to the hides or skins.

It is an object of the invention to provide a method of dehairing orunhairing hides and skins that materially shortens the time of treatmentwithout danger of damage to the hides and that makes possible theproduction of leather and hair of improved quality and texture.

Other objects of the invention will be apparent from the followingdescription.

I have discovered that certain reducing sulphur-oxygen combinations,when added to the unhairing bath, not only act as accelerators todecrease materially the time: required for loosening the hair, but alsomake possible the production of leather of improved quality after thesubsequent operation of hating, puering and tanning.

These sulphur-oxygen combinations are characterized by being stable indry condition and having a substantially greater reducing power insolution than that of the sulphates, sulphites, sulphides orthio-sulphates. While various such compounds may be used, I prefer usingcom- 5 pounds of the class of the hydrosulphites and sulphoxylates andcorresponding organic compounds of sulphur and oxygen. I have found, forexample, that sodium hydrosulphite (nazszoi), sodium sulphoxylate,sodiumformaldehyde sulph- 1o oxylate or zinc calcium hydrosulphite are suitvable and satisfactory.

The compounds referred to may be added to liquid baths or to pastecompositions that can be applied to the hides and skins. The relative 15proportions of the materials used may vary within a considerable range.The reducing sulphur-oxygen compounds may be added in amounts rangingfrom 0.1 to or in some cases from 1 to 10% of the amount of alkali 20added, including lime, caustic soda, sodium carbonate, and so forth orin amounts ranging from 0.05 to 50% or in some cases from 0.1 to 3%,based upon the weight of the cow hides, oat

- skins, sheep skins, calf skins or other hides or skins beingprocessed. The lower portions of the range are most applicable to liquidbaths and the upper portions most applicable to paste compositions.

These ranges are just given by way of ex- 30 ample and even smaller orlarger quantities of these reducing compounds may be. employed dependingupon the character of the hides or skins being treated, the timepermitted for the treatment, the character of the bath or paste utilizedand the ingredients therein, and the temperature at which the treatmentis carried out.

Where the skins and hides are also subjected to treatments withbacterial or enzyme preparao tions, or where sharpening agents areemployed, the amount of the hydrosulphite or sulphoxylate or othercompound may be decreased, but, as a general rule, it is preferable touse between 0.5 and 50 or in some cases between 2 to 10 parts of sodiumhydrosulphite or sodium sulphoxylate or similar compound for everythousand parts of the skins or hides or for every hundred par of lime,which may be employed.

When the reducing sulphur-oxygen com- 50 pounds herein described areused, the result is a substantial decrease the amount of time requiredin the alkaline soaking operation or generally required in the completedehairing process. I

Where sharpening agents, such as sulphides of sodium or arsenic oramines are employed, the action of these sharpening agents is greatlyenhanced by the action of the hydrosulphite or sulphoxylate.

Not only may the reducing sulphur-oxygen combination of the presentinvention be added to the alkaline treating bath, but in addition, itmay be employed in subsequent or in prior treatments accompanying thealkaline treatment as above described, in which case, the hydrosulphiteor sulphoxylate or similar compound may be also included in the alkalinebath in decreased quantities or omitted altogether.

In addition, it is also possible to make pastes of the alkalinematerial, whether it be lime,- soda ash, ammonia or caustic soda and toaddto such pastes suitable quantities of the hydrosulphite orsulphoxylate or similar compound; for example in amounts varying from 1to 50% or more desirably from 1 to 20%. These pastes are then applied orpainted upon the flesh sides of the hides or skins and the hairloosening occurs in a much shorter interval without injuring the hair orthe hides.

Not only is the quality of the skin or hide greatly improved withresultant production of a better grade of leather, but in addition, thehair, which is removed, is of high quality.

In addition to the sodium hydrosulphite or sulphoxylate, it is alsopossible to use the corresponding zlnc, calcium, magnesium, and othersalts and the formaldehyde or other aldehyde and ketone derivatives ofthe hydrosulphites and sulphoxylates.

In addition to the sulphoxylates or hydrosulphites specifically abovementioned, it is also possible to utilize calcium, zinc or magnesiumformaldehyde sulphoxylate, sodium, calcium, magnesium or zinc acetonesulphoxylate, or hydrosulphite, and various other hydrosulphites andsulphoxylates of sodium, calcium, magneslum and zinc. These compoundsmay be added as such, or generated in solution or during the unhairing'process, for example by adding zinc or iron and bisulphite, or byelectrolytic reduction of bisulphite.

In general, all sulphinic or disulphinic acid derivatives whether ofinorganic or organic originaromatic or As a general rule, the sulphurshould at all times be combined with the oxygen to form a reducingcompound or salt having a greater reducing power in aqueous solutionthan is the case with sulphites, bisulphites, sulphides, hydrosulphides,sulphates, thiosulphates and other similar compounds.

While the invention may be carried out in various ways, the followingspecific processes are given by way of examples. They illustrate var-1ous ways of carrying out the invention successfully but it is to beunderstood that the invention is not to be restricted by or limited tosuch exemplifications:

Example 1.1200 pounds of salted cow hides are soaked and then put in apaddle containing a solution of 30 pounds of caustic soda and pounds ofsoda ash with sufiicient water so-that the proportion of skins to waterby weight is about 1 to 4. Then 5 pounds of sodium hydrosulphite areadded and the paddle is operated for a few minutes to obtain a uniformmixture.

After two or three days, the hair is perfectly loosened and may beremoved by unhairing machines in exceptionally good condition.

aliphatic-may be employed.

The skins may then be bated and tanned and the resultant leather is ofvery good quality.

The addition of soda ash is only to prevent exorbitant swelling of skinswith the caustic, but it maybe omitted or replaced by other alkali metalsalts, such as sodium chloride or sodium sulphate.

In carrying out the same operation without the addition ofhydrosulphite, satisfactory loosening of the hair is only obtained aftersix days, and even then, it is not possible to achieve the mostdesirable mechanical unhairing operation. In addition, both the hair andfinal leather are not in as good a condition.

Example 2.--1000 pounds of dry goat skins are soaked for two daysandthen put into a paddle. To the paddle is added pounds of lime and thetemperature is then raised to about 80 F. Then there is added 5 poundsof sodium hydrosulphite, together with 20 pounds of caustic soda. Afterabout two days a perfect hair loosening occurs and the hair and fleshare readily removed by mechanical dehairers or fleshing machines fromthe skins.

The skins and hair after depilation are in excellent condition and thefinal leather, after puering and tanning, is of high quality.

Under the same conditions and with the same reagents in the sameproportions, but with the omission of sodium hydrosulphite, hairloosening is only satisfactorily obtained after ten days and both theremoved hair and the final leather are of inferior quality.

Example 3.-5000 pounds of salted cow hides are soaked for one day andthen to the soaked hides is added about three times their weight ofwater together with 25 pounds of zinc calcium hydrosulphite. Afterseveral hours, there is added 400 pounds of fresh slaked lime and thehides are kept in this solution for about two days. After two days, thehair is sufliciently loosened as to render mechanical depilationrelatively easy and the hair and unhaired pelts are in good condition.

Without the hydrosulphite, the loosening .of

the hair and the unhairing operation is unsatisfactory, even though thehides are kept in a bath for over four days.

Example 4.10 dozen sheep skins are soaked and-then painted upon theflesh side with a paste containing lime and 5% sodium hydrosulphite. Thepainted skins are kept in moist condition for twenty-four hours. Thewool then is readily removed by pulling. The wool and the pelt are bothin excellent condition. The saving in time is substantial.

Example 5.1000 pounds of goat skins by dry weight are soaked for twodays and then put into a solution of 6000 pounds of water containing 35pounds of caustic soda. To this solution is then added two pounds ofsodium form-' 'zymatic dehairing preparation of bacterial origin. Aftertwelve hours; the skins are capable of being dehaired most readily andboth the hair and the pelt are in excellent condition.

Example 6.500 pounds of salted calf skins are washed in a paddle for tenminutes and then soaked in water containing 2% pounds of sodiumhydrosulphite and 3 pounds of ammonia. When the hair commences to slipafter twenty-four hours, 50 pounds of lime are added and after anothertwenty-four hours, theskins are taken out and mechanically unhaired.

Example 7.-1000 pounds of dry goat skins are soaked for two days andthen put in a paddle so that the proportion of goat skins to water isabout 1 to 8 by weight.

Then there is added. pounds of sodium hydrosulphit'e. After one hourthere is further added 120 pounds of fresh slaked lime and 2 pounds ofsodium sulphide.

After forty-eight hours the hair loosening has set in to such adegreethat the hair may be removed with a brush.

Instead of sodium sulphide, other sh-arpeners' might be employed, suchas red arsenic and amines.

As amines there may be used mono-, dior triethanolamine, ethylormethyl-amines, diaminopropanol, various hydroxy-, carboxyor othersubstituted amines.

In carrying out the above processes, it is found that various antisepticagents may be readily included without hindering the action of thereducing sulphur-oxygen combination, such antiseptic agents being, forexample, phenols, cresols, naphthols, various halogenated or chlorinatedbenzene, toluene, xylene or naphthalene derivatives, pine oil or otherterpene derivatives, and so forth.

As enzymatic products in the above procedures, there may be utilizedenzymes, such as pancreatin, trypsin, papain, kathepsin, bromelin orenzymes derived by the growth and cultivation of bacteria, fungi andmolds, such as B. subtilis, B. mesentericus, mycoides and Ziquefaciens,Aspergillus oryzae or niger, Penicillz'um glaucum, Mucor delemar ormucedo, Amylomyces rouxii, Tryotria: tenuis and so forth.

Many other changes could be effected in the particular features ofprocess and treatment disclosed and in specific details thereof, withoutsubstantially departing from the invention intended to be defined in theclaims, the specific description herein merely serving to illustratevarious ways of successfully carrying out the invention.

What is claimed is:

1. A process of loosening the hair of skins and .hides which comprisessubjecting said skins or hides to treatment with an alkaline materialand to the action of a compound selected from the group consisting ofhydrosulphites, sulphoxylates and their organic derivatives.

2. A process of loosening the hair of skins and hides which comprisestreating the skins or hides with an alkaline bath containing a compoundselected from the group consisting of hydrosulphites, sulphoxylates andtheir organic deriva- 4 tives.

, ations which ,comprises adding a hydrosulphite to the bath.

5. A process of aiding the loosening of hair of skins and hides inalkaline soaking operations which comprises adding a sulphoxylate to thebath.

6. A process of accelerating the loosening of hair of skins and hides inalkaline soaking operations which comprises adding a formaldehydesulphoxylat'e to the bath.

'7. A process of loosening the hair of skins and hides which comprisesimmersing the skins or hides in a bath containing an alkaline materialand a hydrosulphite, about 0.1 to 70 parts of the hydrosulphite beingutilized for every 100 parts of said alkaline material.

8. A process of looseningthe hair of skins and hides which comprisesimmersing skins or hides in a bath containing lime and a hydrosulphite,between 0.05 to 50 parts of the hydrosulphite being included for aboutevery 100 parts by weight of the skins or hides.

9. The process of loosening the hair of skins and hides which comprisesapplying to the flesh sides of said skins or hides a paste of analkaline material including an accelerator selected from the groupconsisting of hydrosulphites, sulphoxylates and their organicderivatives.

10. A process of loosening the hair of skins and hides which comprisesapplying to the flesh sides of the skins or hides a paste of limecontaining about 1 to 50% of sodium hydrosulphite.

11. A process of dehairing skins and hides which comprises soaking theskins or hides in water, then causing loosening of the hair by immersingthe skins or hides in an aqueous bath containing lime and caustic sodaand a hydrosulphite, and then removing the skins or hides andmechanically removing the hair.

12. A hair-loosening composition comprising lime and a hydrosulphite.

13. A hair-loosening composition comprising caustic alkali and asulphoxylate.

14. A hair-loosening composition comprising an alkaline materialselected from the group consisting of caustic soda and lime, asharpening material selected from the group consisting of sodiumsulphide, red arsenic and an amine, and an accelerator selected from thegroup consisting of hydrosulphites, sulphoxylates and their organicderivatives.

15. A hair-loosening composition comprising soda ash and ahydrosulphite.

16. A process of loosening the hair of skins and hides which comprisessubjecting said skins or hides to the acttion of an enzyme, an alkalinematerial and a compound selected from the group consisting ofhydrosulphites, sulphoxylates and their organic derivatives.

17. In the process of loosening the hair of skins and hides by theaction of lime the improvement which comprises adding to the lime ahydrosulphite of the group consisting of alkali and alkaline earthhydrosulphites.

18. In the process of loosening the hair of skins and hides by theaction of lime the improvement which comprises adding to the lime analkali hydrosulphite.

19. In the process of loosening the hair of skins and hides by theaction of lime the improvement which comprises adding to the lime sodiumhydrocompound selected from the group consisting of hydrosulphites,sulphoxylates and their organic derivatives.

22. A hair-loosening composition comprising an alkaline materialselected from the group consisting of caustic soda and lime and anaccelerator selected from the group consisting of hydrosulphites,sulphoxylates and their organic derivatives.

23. A process of-loosening the hair of skins and hides which comprisestreating the skins or hides with an alkaline bath containing asharpening 7 material selected from the group consisting of sodiumsulphide, red arsenic and an amine, and f-

